As a semiconductor device requires a high speed, miniaturization of a wiring pattern, and high integration, it has recently been required to reduce capacitance between wirings, and improve conductivity of a wiring and electromigration resistance. Accordingly, a technology on a copper multilayer wiring is spotlighted which uses a copper (Cu) as a wiring material having a higher conductivity and a higher electromigration resistance than aluminum (AL) or tungsten (W). The copper multilayer wiring technology uses a low dielectric constant layer (low-k layer) film as an insulating film between the layers.
As a copper film forming method of a copper multilayer wiring, there are known physical vapor deposition (PVD) such as sputtering, plating, and metal organic chemical vapor deposition (MOCVD) using a vaporized organic metallic raw material. However, the PVD method has a problem of a poor step coverage, and of a difficulty in embedding in a fine pattern. In the plating method, due to an additive included within a plating solution, the copper film includes a large amount of impurities. In the MOCVD method, while it is easy to achieve a good step coverage, it is difficult to improve film quality because a large amount of impurities, such as carbon (C), oxygen (O), fluorine (F), resulting from a side chain group coordinated to a Cu atom, remain in the copper film. Also, the raw material is relatively expensive because the side chain group coordinated to the Cu atom has a complicated structure. Further, due to the thermal instability and a low vapor pressure, it is difficult to stably supply a raw material gas.
Meanwhile, Japanese Patent Laid-Open Publication No. 2004-27352 (patent document 1) discloses a technology for forming a copper film, in which a CuCl plate is placed within a chamber, and is etched by generating Ar gas plasma so as to generate desorbing species of CuCl, and generate dissociation species of Cu and Cl from the desorbing species by Ar gas plasma. And then, the temperature of a substrate is reduced to lower than the temperature of the plate so as to form the copper film on the substrate by direct reduction. Through the technology, it is possible to use an inexpensive raw material with a high film-forming speed, and to form a copper film that includes relatively less impurities therein.
However, in the technology in the patent document 1, there is a concern that it is difficult to completely remove Cl in the copper film, and thus a trace element of Cl may remain in the copper film. Even a trace element of Cl may cause an increase in wiring resistance and a reduction in the reliability, accompanied by the corrosion of a copper wiring. Also, since a substrate surface is exposed to plasma at an initial stage of film formation, the substrate may be subjected to a chemical or physical damage. Especially, a Low-k film used as a wiring is likely to be subjected to an increase in a dielectric constant by the plasma, and destruction of a fine structure (plasma damage). Also, since the plasma sputters other members than the CuCl plate within a reactor, the sputtering causes a damage to the members, impurities in the film by sputtered particles, and contamination. Accordingly, the application of the technology disclosed in patent document 1 to the copper multilayer wiring has a problem in that it requires expensive devices or materials to solve the above described problems.
Meanwhile, thought it is not directed to a semiconductor manufacturing process, Japanese Patent No. 2745677 (patent document 2) discloses a method for manufacturing a copper wiring by using an inexpensive raw material which is different from a wet plating. In this method, an inexpensive organic Cu compound such as copper (II) formate (Cu(OCHO)2) or a hydrate thereof, is applied to a substrate, and heat is provided thereto in a non-oxidizing atmosphere so as to form a copper thin film. Also, there is a report (non-patent document 1) on the formation of a copper wiring in A. Gupta and R. Jagannathan, Applied Physics Letters, 51(26), p 2254, (1987), in which copper (II) formate dehydrate applied to a substrate is heated by a laser beam with a narrowed beam diameter. All of the above described methods use a thermal decomposition reaction of copper (II) formate to form the copper film. In the above described methods, although it is possible to form a metal (Cu) film at a low cost, it is inappropriate to embed a metal in a nanometer-level fine shape, such as in an ultra large-scale integrated (ULSI) wiring, and the electric conductivity is not higher than that of original copper film.
There is a report on an attempt to use an inexpensive copper (II) formate hydrate as a raw material of MOCVD in M. J. Mouche et al, Thin Solid Films 262, p 1˜6, (1995) (non-patent document 2). Powder of copper (II) formate hydrate is put into a raw material container and then is heated with an introduction of a carrier gas. The carrier gas carries a vaporized component generated by the heating, to the surface of a heated substrate disposed within another reactor via a pipe. The carried vaporized component is thermally decomposed on the substrate surface to generate a copper film.
It is known that the vaporized component generated within the raw material container is copper formate in A. Keller and F. Korosy, Nature, 162, p 580, (1948) (non-patent document 3). Also, according to the reaction scheme represented by Formula (1) below, a gas state copper formate (Cu(OCHO)) which is volatile is generated from non-volatile copper (II) formate, and is carried to a substrate:2Cu(OCHO)2→2Cu(OCHO)+CO+CO2+H2O   (1)
Since copper formate, as reported in non-patent document 3, is a material that can be thermally-decomposable very easily, a copper thin film is easily formed from copper formate at a low temperature according to the reaction scheme represented by Formula (2) below:2Cu(OCHO)→2Cu+2CO2+H2   (2)According to this method, it is difficult for a formate group (OCHO) as a ligand to be introduced in the copper film because it is likely to be exhausted through thermal decomposition into CO2 or H2. Thus, it is easy to form a high purity copper film excluding impurities. However, in general, a method for carrying a component vaporized from a solid raw material by a carrier gas is significantly influenced by a thermal conductivity within a solid raw material container maintained under a reduced pressure. Furthermore, it is difficult to stably supply the vaporized component. Also, copper (II) formate as a raw material within the solid raw material container may be thermally decomposed, thereby forming a copper film in the container. In other words, the raw material may be easily deteriorated.
Also, according to the non-patent document 3, silver may be used as a metal which can form metal formate and can show the same reaction as that of copper, and may form a silver film as a wiring layer in the same manner as that in the copper film, but has the same problem as that in the copper film.